Two U.S. cybersecurity companies say their analyses of a hack on the computers of a Democratic Party fund-raising group shows Russian hackers to be responsible.

The two American firms said in statements on August 1 that the Internet domains and registrants used to hack the Democratic Congressional Campaign Committee computers point to a Russian hacking group, Fancy Bear, that is linked to Russian intelligence services.

Fancy Bear was also connected to the breach of computers used by the Democratic National Committee (DNC) in June, said the firms, Fidelis Cybersecurity and ThreatConnect.

The DNC case ignited a controversy within the U.S. presidential race when Democratic nominee Hillary Clinton accused Russian hackers of involvement.

In a July 31 interview, Clinton said, "We know that Russian intelligence services hacked into the DNC."

The Kremlin rejected allegations it was behind the DNC computer hack.

Sensitive DNC e-mails were later released by WikiLeaks, leading to the resignation of DNC Chairwoman Debbie Wasserman Schultz.

Kremlin spokesman Dmitry Peskov said on August 1 that Clinton's comments were "of the preelection rhetoric genre."

"In this case," Peskov said, "[the Americans] are trying to camouflage some of their own [preelection] shenanigans by demonizing Russia.”

The United States has not publicly accused Russia of being behind the hack of Democratic Party computers, but U.S. officials said they believe Russia engineered the release of the e-mails to influence the November 8 U.S. presidential election.